Sloths are masters of living life in the slow lane. These tree-hugging mammals, split into two-toed and three-toed varieties, travel only about 125 feet a day — so slowly that moss and algae grow on their fur. This lethargic lifestyle is actually a survival strategy suitable for their slow metabolisms and low-calorie diets, which are mostly based on tree leaves. In fact, three-toed sloths have the slowest metabolism of any mammal (followed closely by pandas and two-toed sloths). 

Their sluggish metabolism, as well as their ability to slow their heart to one-third its normal rate, give sloths an unexpected superpower — they can hold their breath for an impressively long time. With estimates suggesting that some two-toed sloths can hold their breath for upwards of 40 minutes, this makes sloths better at conserving oxygen than even some marine mammals such as dolphins, who can only hold their breath for 15 minutes, max. The sloth breathing technique, aided by the design of their lungs, helps make sloths excellent swimmers. So while their leisurely lifestyle may seem a bit lazy to the untrained eye, don’t blame the sloths — they’re just built that way.